Method for improving glass adherence to gold film

ABSTRACT

A METHOD FOR IMPROVING THE ADHERENCE OF GLASS TO A GOLD FILM IS DISCLOSED. A LAYER OF A METAL SUCH AS TANTALUM IS DEPOSITED ON THE GOLD FILM. THE METAL LAYER IS HEATED IN AN OXIDIZING ATMOSPHERE TO CONVERT THE METAL TO A METAL OXIDE. A LAYER OF GLASS IS THEN DEPOSITED ON TOP OF THE METAL OXIDE LAYER.

Aug. 27, 1974 METHOD FOR IMPROVING GLASS ADHERENCE TO GQLD FILM FIG.

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L. E. TERRY 3,8

Original Filed July 24, 1970 T0205 Au Si 02 T0205 Au United StatesPatent 3,832,230 METHOD FOR IMPROVING GLASS ADHERENCE TO GOLD FILM LewisE. Terry, Phoenix, Ariz., assignor to Motorola, Inc., Franklin Park,Ill.

Original application July 24, 1970, Ser. No. 58,102. Divided and thisapplication Mar. 6, 1972, Ser. No. 231 812 Int. Cl. B44d 1/14, 1/18;C03c 15/00 U.S. Cl. 117-217 4 Claims ABSTRACT OF THE DISCLOSURE A methodfor improving the adherence of glass to a gold film is disclosed. Alayer of a metal such as tantalum is deposited on the gold film. Themetal layer is heated in an oxidizing atmosphere to convert the metal toa metal oxide. A layer of glass is then deposited on top of the metaloxide layer.

CROSS REFERENCE TO A RELATED APPLICATION This is a division ofapplication, Ser. No. 58,102, filed July 24, 1970.

BACKGROUND OF THE INVENTION Gold films are used as metal contacts insemiconductor devices and particularly in integrated circuit devices. InLSI (Large Scale Integrated Circuits) multilayer metallization isrequired in the integrated circuit structures. In order for themultilayer metallization to be effective, there must be a layer ofinsulation such as glass between the gold layers. Problems separatingtwo or more layers of gold have arisen due to the lack of satisfactoryadherence of the glass insulating layer to the gold film. Failure of theglass to adhere satisfactorily to the gold film causes the glass layerto peel or flake 01f thereby resulting in device failure.

SUMMARY OF THE INVENTION It is an object of this invention to provide amethod for improving the adherence of glass to gold films.

It is another object of this invention to provide a method of providingmultilayer metallization for integrated circuits.

These and other objects are accomplished in accordance with thisinvention by a method in which a metal such as tantalum, zirconium,niobium or hafnium is deposited on the gold fihn. The metal film, forexample, tantalum, is then heated in an oxidizing atmosphere to formtantalum oxide. A layer of glass is then deposited over the tantalumoxide. The glass adheres to the tantalum oxide which in turn adherestightly to the gold.

In a preferred embodiment of this invention, after selectively providingopenings in the glass and tantalum oxide layers, a second layer of goldis deposited, then a second layer of tantalum is deposited thereon andconverted to tantalum oxide. A second layer of glass is also depositedon the tantalum oxide.

These steps may be repeated as often as required for the multilayermetallization system.

IN THE DRAWING FIGS. 1 through 5 show the various steps of the processin accordance with this invention.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENT Referring now to the drawings,FIG. 1 shows a substrate of an insulator or ceramic material such asalumina. Substrate 10 may be a semiconductor such as silicon, germanium,or any of the group 35 semicon- 3,832,230 Patented Aug. 27, 1974 ductorssuch as gallium arsenide, gallium antimide, gallium phosphide, indiumantimide, indium phosphide and aluminum arsenide. On top of thesubstrate 10 is a gold layer 12. If the substrate is silicon, a layer ofsilicon dioxide (not shown) is required to separate the silicon from thegold layer 12. The gold layer 12 is deposited and etched to form anopening therein by conventional deposition and etching techniques.

As shown in FIG. 2, a layer of metal 14 is formed on top of the goldlayer 12. The layer 14 is of any metal taken from the group consistingof titanium, zirconium, tantalum, tungsten, niobium and hafnium. Thepreferred metal is tantalum and the invention will be hereinafterdescribed in terms of the tantalum.

The tantalum layer 14 is covered with a layer of photoresist (not shown)as is well known in the arts to provide a mask so that the metal layer14 may be etched. The tantalum layer 14 is about to 1000 angstroms thickso that it can be easily etched at room temperature with a conventionalmetal etchant, for example, an etchant containing equal quantities ofhydrofluoric acid and nitric acid to form the openings 16 and 18 asshown in FIG. 3. The photoresist layer (not shown) used to form theopenings 16 and 18 is then removed. The tantalum layer 14 is oxidized atan elevated temperature to form the tantalum oxide layer 20. Thetantalum oxide layer 20 is easily obtained by heating the device in anoxygen atmosphere at temperatures between 450 and 750 C.

The heating of the metal in an oxidizing atmosphere to form metal oxideresults in some of the metal ditfusing or migrating into the gold filmthereby forming a more adherent bond. For example, some of the tantalumin layer 14 diffuses into gold layer 12 while the rest of the tantalumin layer 14 is being oxidized to form tantalum oxide. It is thediffusion at an elevated temperature of the tantalum into the gold filmwhich is believed to cause the improved adherence between the gold filmand the subsequent layer of glass. This invention is not limited to thistheory, however.

A layer of glass or another dielectric 22 is deposited on top of thetantalum oxide layer 20. When silicon dioxide glass is used, a stream ofsilane and oxygen are passed over the wafer while the wafer is at anelevated temperature of 200 to 750 C. A layer of silicon dioxide is thepreferred dielectric although aluminum oxide, silicon nitride and dopedglasses may be used. Using conventional etching techniques, openings 24and 26 are etched through the silicon dioxide layer 22. A metal contactor film (not shown) may be deposited in the openings 24 and 26 makingcontact to the gold film 12 to provide a multilayer metallization systemsuitable for use in integrated circuits.

In a preferred embodiment, gold is deposited in openings 24 and 26. Thissecond layer of gold is protected from scratching, tweezer marking andprobe markings by a coating of glass. The coating of glass is made toadhere to the gold layer by the use of the tantalum oxide bonding layerheretofore described.

What is claimed is:

1. A method for improving the adherence of glass to gold film comprisingthe steps of:

depositing a layer of a metal taken from the group consisting oftantalum, niobium, zirconium, titanium and hafnium on a layer of gold,

heating the metal in the oxidizing atmosphere to convert the entiremetal layer to a metal oxide layer, and depositing a layer of glass ontop of said metal oxide layer.

2. A method as described in claim 1 wherein said metal is tantalum.

4 3. A method as described in claim 1 wherein said metal titanium insaid openings on said exposed gold suris deposited as a layer having athickness of about 100 to face. a 1000 Angstroms. References Cited 4. Amethod for improving adherence of glass to glass UNITED STATES PATENTSfilm comprising the steps of: 5

depositing a layer of metal taken from the group con- 3,256,583 6/1966siki et 1 117-217 sisting of tantalum, niobium, Zirconium, hafnium3,268,773 8/1966 Valley 117217 and titanium on a layer of gold;3,274,024 9/ 1966 Hill et a1 117-2l7 forming selected openings in themetal layer whereby 3,581,161 5/1971 Cunningham et :11.

said gold layer is exposed; 1O 317-235/465 heating the metal in anoxidizing atmosphere to convert 3,690,945 9/ 1972 Kuisl 317 235/46 5 theentire metal layer to a metal oxide layer; 3,698,946 10/ 1972 Kaspaul etal. 117-217 depositing a layer of glass on top of said metal oxide andsaid exposed gold surface; CAMERON K. WEI FFENBACH, Primary Examineretching openings in said glass layer to expose the gold 15 U S C1 XRsurface previously exposed, and; depositing a metal selected from thegroup consisting of 70 70 317 gold, tantalum, niobium, zirconium,hafnium and

